Chemical composition for acid hardening photographic fixing baths



Patented Sept. 10, 1940 UNITED STATE CHEMICAL COMPOSITION FOR ACID HARD-ENING PHOTOGRAPHIC FIXING BATHS Lawrence J. Webster, Rochester,

N. Y., as-

signor to Defender Photo Supply 00., Inc., Y Rochester, N. Y., acorporation of New York No Drawing. Application September 11, 1939,Serial No. 294,298

2 Claims.

This invention relates to photographic baths, with more particularreference to acid hardening fixing baths, and has for its principalobject to provide a mixture of chemicals that can be pack- 8 aged andmerchandised in a dry state; and which has pronounced advantages overdry mixtures heretofore used for this purpose. More particularly, theobject of the invention is to afford a mixture of dry chemicals which is10 stable under atmospheric changes and not subject to interaction uponeach other while in a dry state due to moisture, preventing caking andconsequent loss of efiiciency by the breakdown of some of theingredients, the mixture forming the 18 subject matter of the inventionbeing either entirely free from water of crystallization or so composedthat it is less seriously affected by any water of crystallizationpresent, thus increasing the useful life and efficiency of thecomposition.

20 In one aspect, the invention is designed to eliminate entirely waterof crystallization in the mixture by using only anhydrous compounds,andin addition to preventing detrimental caking of the dry powderedmass, the invention has for a further objective to afford a mixturewhich when dissolved in water may possess greater gelatinhardeningqualities than materials heretofore used and will resist sludging orprecipitation of aluminum compounds orother non-solubles upon o additionof alkali resulting from developer solutions, and with a minimum changein its pH value or the acid ion concentration of the solution.

Acid hardening photographic fixing baths have been produced by combininga silver halide solvent such as sodium thio-sulfate, a preserving agentsuch as sodium sulfite, a suitable acidifying agent such as acetic acidor sodium acid sulfite, and a hardening agent such as aluminum potassiumsulfate, and I have found that by the 40 addition of dextro-gluconic,acid, mucic acid, or other derivative of a hexose, precipitation of theinsoluble compounds upon addition of alkaline developing solution ismore effectively prevented throughout the full life of the bath or untilthe soiium thiosulfate -is exhausted, the hydrogen ion concentration orpH value of the bath is properly maintained for photographic purposes,andcapable of producing gluconic or mucic ions in solution.

The invention involves the use of gluconic acid, mucic acid, or saltsthereof, or other derivative of a hexose, as a constituent part of a dry5 chemical mixture thatis dissolved in water to produce a photographicacid fixing bath having proper gelatin-hardening and non-sludgingcharacteristics. Such a dry mixture which in other respects is composedof the chemicals con- 10 ventionally used in such photographic fixingbaths may be variously formed, and the following are given as merelyillustrative of several formulas that may be successfully used, andwhich incorporate the invention: 15

Formula No. 1

- Grams Sodium thiosulfate (anhydrous) 120 Sodium bisulfite (anhydrous)30 an Aluminum gluconate 30 This affords a dry mixture suitable fordissolving in a quantity of water to make one liter of acid fixingsolution.

Formula N0. 2

Grams Sodium thiosulfate (anhydrous) 120 Sodium bisulfite (anhydrous) 30Sodium gluconate 4.5 Potassium aluminum sulfate 15 Formula. No. 3

Grams Sodium thiosulfate (anhydrous) 120 Sodium bisulfite (anhydrous) 30Mucic acid a. 3 85 Potassium aluminum sulfate 15 derived fromcarbohydrates of the sugar type, 50

such as a hexose or pentose, including for instance dextro-saccharicacid, levuo-idonic acid, and dextro-arabonic acid.-

The above proportions are not critical and may be varied, and thedisclosure of this application may be otherwise modified in practicewithout departing from the spirit of the invention or the scope of thefollowing claims.

I claim:

1. A dry'mixture of chemicals which when dissolved in water produces anacid hardening photographic fixing bath; including a silver halide

